CONTROLLED INFILTRATION OF LEACHATE CONCENTRATES
INTO LANDFILL BODIES
EXPERIENCES AND SOLUTIONS
Dr. Hartmut Eipper
Pall GmbH Wassertechnik
Philipp-Reis-Straße 6, D – 63303 Dreieich, Germany
INTRODUCTION
Direct leachate circulation has been practised for a long time as a measure to get rid of leachate
for which no appropriate equipment for treatment is available. However, in temperate climate
regions natural evaporation is never enough to prevent the steady increase of water volumes
generated in the landfill. Well-considered concepts therefore restrict recirculation to infiltration
of part of the leachate in order to provide for a proper water management in the landfill. In
domestic waste landfills, infiltration leads to an increased biological activity resulting in a
considerably higher production of landfill gas and faster mineralisation of organic matter. This
has a positive impact on the duration of the after care period after closing of the landfill. The
further development of this concept leads to a combination of leachate treatment with the landfill
water management: If landfill leachate is treated by Reverse Osmosis, the concentrate may be
used for infiltration. The recovery rate of the permeate controls the amount of concentrate which
may be adapted to the requirements of the specific landfill (fig. 1).
By the raised concentration of leachate contents in the concentrate, the biochemical and physical
processes are enhanced. The main processes are:
-
biochemical decomposition processes in the landfill body
decomposition of organic and inorganic material in the form of oxides, sulphides and
carbonates
adsorption of heavy metals at different inner surfaces in the waste body
crystallisation processes
arising of carbonates, sulphides and sulphates by inorganic-chemical processes
Figure 1. Water Management by Leachate Treatment
REQUIREMENTS FOR INFILTRATION
For these reasons, infiltration of leachate and concentrates is common practice in many
countries. However, in some countries this process is looked at critically or it is limited by
approval authorities within special boundary conditions.
The main concern is the danger of ground contamination by these liquids due to channelling and
local air pollution by contact with the atmosphere.
Experiences in the past have demonstrated that improper design of infiltration may lead to
undesirable results. Therefore a couple of measures are usually required by approval authorities
(fig. 2):
- Efficient bottom lining is to prevent penetration of liquids into the ground if channelling
occurs
- An appropriate drainage system is to collect leachate and prevents accumulation of water
within the landfill body
- Solidity of the landfill body itself, depending on the type of refuses, humidity and way of
disposing
- Relevant amount of organic waste
The landfill must be effective as bioreactor to make use of humidification for biochemical
decomposition processes
- A degasification system is to provide for gas extraction from the landfill body
- Control of gas and water balances must be achieved by appropriate control and
monitoring systems
- The landfill height must not fall below a minimum (e.g. 10m) in order to enable
horizontal distribution of the liquid
Figure 2. Preconditions Required by Authorities
The majority of these points refers to liquid distribution and avoidance of preferential flow
channelling. Fortunately a landfill is a complexly composed waste body which exhibits
principally branched flow paths without direct channels down to the bottom. Figure 3 shows the
liquid flow within a landfill body under conditions of equally distributed paths. Preferred
directions should occur neither horizontally (overflow at slope) nor vertically (channelling and
liquid accumulation at the bottom). The a.m. concerns require some basic design considerations
which are compiled in figure 4:
-
Avoidance of channelling and local super saturation by means of a proper liquid
distribution system
To prevent air pollution through odors and aerosols, the liquid should not be sprinkled
over the landfill but percolated into the surface or under the cover
The dimensioning of pipes and fittings should be suitable for cleaning and rinsing
During standstills the concentrate must be replaced by clear water to prevent scaling in
the pipes
Figure 3. Flow Paths in the Landfill Interior
Figure 4. Basic Design Requirements
TECHNICAL SOLUTIONS FOR INFILTRATION
“Controlled infiltration” implicates technical equipment that enables the change of position of
liquid feed. This flexibility must be ensured, as the optimisation of adjustment, control and
monitoring of infiltration parameters may vary with long-time effects.
Figure 5. Horizontal Infiltration System
Figure 6. Vertical Infiltration System
Examples for such technical equipment are horizontal systems with several drain lines (figure 5).
In cases where the arrangement of layers in the landfill body may prevent proper penetration,
vertical irrigation systems with lances may be applied (figure 6).
Figure 7. Trickling Bed with Gravel Filling
Figure 8. Trickling Well
Another proposal for horizontal distribution is shown in figure 7. The gravel bed provides equal
distribution of the liquid over the whole area. The gravel should not contain calcium carbonate,
because the sulphate content in the liquid would lead to gypsum formation with blocking of flow
paths.
A corresponding proposal for a more vertical solution is presented in figure 8. A drainage well
filled with gravel is the measure for the distribution of the liquid.
A totally different approach to the solution of the distribution process is shown in figure 9. In
this case the liquid is mixed with waste before it is placed into the landfill. This distribution of
liquid is perfect and channelling may be safely prevented.
However this method requires an additional step before dumping the waste. Moreover, enough
waste has to be available to absorb the liquid.
Figure 9. Mixing before Disposal
A practical example for a modern infiltration system is presented in figure 10. It refers to the
landfill Algar in Portugal where nearly two years ago a leachate treatment with RO and
concentrate infiltration was installed.
Figure 10. Example: Infiltration Algar
Max. 37,4 m³/d are trickled onto an area of approx. 1250 m². Whether this area is sufficient will
be seen in the future (fig. 11 and 12).
Figure 11. Distribution Network
Figure 12. Controlled Reinjection of Concentrate
In the landfill Valnor in France, a by far smaller amount of concentrate is sunk by two
rectangular blocks (fig.13). The design aims at a vertical infiltration (fig. 14 and 15).
Figure 13. Example: Infiltration Valnor
Figure 14. Trickling Body
Figure 15. Sectional View
RESULTS FROM LANDFILLS WITH INFILTRATION
The two cases in Portugal and France mentioned before, are too recent to make any substantial
statements on their function. However, a couple of long-term monitored experiences are
available from landfills with infiltration in Germany. Furthermore two scientific publications
have dealt with the behaviour of landfill waste with controlled injection on laboratory resp. small
technical scale (Henigin 1999; Albrecht 2001). These investigations have shown that the gas
production is enhanced. On the other hand the major parameters such as COD, ammonia and
TOC remained constant during the reinjection period. Any further concentration of these or other
components could not be observed. Concerning the increase of the leachate amount by
concentrate injection it has been proven that an unlimited accumulation of leachate is not
possible under these conditions. The maximum increase remains between 10-30% depending on
the recovery rate of the reverse osmosis treatment system (Henigin 1999).
Some preliminary results referring to experiences with concentrate infiltration on a commercial
scale have similarly demonstrated that the impact of concentrate recirculation on the composition
of leachate is limited (Eipper, Maurer 1999).
Meanwhile more data have been collected and longer periods for assessing the impact of
concentrate injection are available.
Before assessing the trends for major parameters such as e.g. conductivity, COD, ammonia, it
may be interesting to look at the curves for a landfill without infiltration (fig. 16). It becomes
clear that the a. m. major parameters fluctuate considerably depending on seasonal conditions
and special features of landfill operation. This landfill is filled with domestic waste with a height
of 25m.
Figure 16. Main Parameters without Infiltration
The next diagram (fig. 17) presents the same parameters for the landfill of Rastatt in Germany.
On this landfill a RO-system has been installed in 1986 for the purification of leachate. It was the
first one in Germany. This landfill disposes of an area of 12,4 ha with a max. height of 60m and
is filled with domestic waste. The leachate production varies between 30.000-50.000 m³/d and
the RO-system achieves a permeate output of approx. 70%. The concentrate is pumped through
PE-pipes to 8 drainage wells, filled with gravel, which are 15-20m deep. They are fed
alternately.
When looking at the diagram more closely a peak for the parameters in 1995 becomes obvious.
This was due to the removal of a part of the preliminary cover. As simultaneously the leachate
amount increased, it appears that a washing out process is happening in the corresponding part of
the landfill body.
The presented section from 1993-2000 does not show any significant trend for the various
parameters. It is remarkable that this is valid for the sulphate concentration as well, although
sulphuric acid was added for pH-decrease before RO-treatment. This effect may be explained by
the anaerobic condition in the landfill body by which sulphate is reduced to sulphide and then
immobilized as e.g. FeS (Albrecht 2001).
Figure 17. Main Parameters Landfill Rastatt
Another example (fig. 18) is presented from a landfill in Northern Germany where infiltration
has been practised since 1992. A section covering the years 96-98 again shows mainly seasonal
effects with strong variation in conductivity, ammonia and COD. However, no specific trend
may be observed. Again the sulphate concentration remains constant.
Figure 18. Main Parameters Landfill North Germany
A direct comparison between parameter curves (fig. 19) before and after the start of concentrate
infiltration is presented from a landfill near Hanover. This landfill has been in operation since
1968. The RO-Treatment started in 1992 with preceding biological treatment.
The concentrate is distributed by a trickling hose which is moved every 100 h.
Figure 19. Main Parameters Landfill with and without Infiltration
SUMMARY
The background for the feasibility of concentrate reinjection is the fact that a landfill can usually
be compared with a bioreactor which produces an important amount of gas on optimised
operating conditions. As the organic part of a landfill decreases with the increased gas
production, the time interval for the immobilising of waste material in the landfill can be
reduced. This process may be accelerated by additional humidity introduced via concentrate
injection.
Scientific studies have shown that the injection of concentrates has no striking detrimental
effects on the long-term behaviour of the leachate concentrations. This has been attributed to the
following main reasons:
•
•
Biochemical degradation processes take place inside the landfill
Deposit and fixation of organic and inorganic compounds in the landfill body
To avoid problems such as channelling and odor formation, infiltration must be performed in a
controlled way. The term “controlled infiltration” describes engineering solutions for the
infiltration of water into the landfill body, which can be monitored, controlled and optimised.
Depending on the specific landfill conditions a variety of technical solutions is available which
allow tailor-made solutions.
Many landfills with RO leachate treatment systems and infiltration of concentrate have already
been in operation for a couple of years without significant problems. The development of key
parameters in the course of the years demonstrates that the composite of raw leachate is not
significantly influenced by concentrate reinjection.
FIGURES
(1) Water Management by Leachate Treatment
(2) Preconditions Required by Authorities
(3) Flow Paths in the Landfill Interior
(4) Basic Design Requirements
(5) Horizontal Infiltration System
(6) Vertical Infiltration System
(7) Trickling Bed with Gravel Filling
(8) Trickling Well
(9) Mixing before Disposal
(10) Example: Infiltration Algar
(11) Distribution Network
(12) Controlled Reinjection of Concentrate
(13) Example: Infiltration Valnor
(14) Trickling Body
(15) Sectional View
(16) Main Parameters without Infiltration
(17) Main Parameters Landfill Rastatt
(18) Main Parameters Landfill North Germany
(19) Main Parameters Landfill with and without Infiltration
REFERENCES
Peters, Th., ”Biodegradation and Immobilisation in the landfill body based on controlled
Infiltration of Leachate Concentrate”, Proceedings SARDINIA 2001, Eight International Waste
Management and Landfill Symposium, Vol. II, pp. 123-132, October 1995
Bendz D., Singh V.P. and Berndtsson R.: “The Flow Regime in Landfills – Implications for
Modelling”, Proceedings SARDINIA 97, Sixth International Waste Management and Landfill
Symposium, Vol. II, pp. 97-108, October 1999
Eipper, H. and Maurer C.: “Purification of landfill leachate with membrane filtration based on
the Disc Tube DT”, Proceedings SARDINIA 99, Seventh International Waste Management and
Landfill Symposium, Vol. II, pp. 97-108, October 1999
Heyer, K.H. and Stegman, R.: “New experiences with Drying Effects in Covered Landfills and
Technical Methods for Controlled Water Addition”, Proceedings SARDINIA 99, Seventh
International Waste Management and Landfill Symposium, October 1999
Henigin, P.: Auswirkungen der Konzentrat-Rückführung nach der Membranfiltration auf die
Sickerwasserneubildung von Hausmülldeponien (Thesis), Beiträge zur Abfallwirtschaft, Band
11, Technische Universität Dresden, 1999
Albrecht, B.: Großlysimeter-Langzeit. Untersuchungen zur Rückführung von UmkehrosmoseSickerwasserkonzentrat auf den Deponiekörper von Hausmülldeponien unter „FlushingBedingungen" (Thesis), Stuttgarter Berichte zur Abfallwirtschaft; Band 80, Universität Stuttgart,
2001